Action Points

Note that this observational study of patients with paroxysmal atrial fibrillation found that stroke risk was elevated with greater burden of atrial fibrillation.

This suggests that anticoagulation should be strongly considered among paroxysmal AF patients with risk factors for stroke.

A greater burden of even intermittent atrial fibrillation (Afib, or AF) was associated with a significantly higher stroke risk and could warrant anticoagulation, according to a retrospective study of continuous ambulatory heart monitoring data.

Compared with paroxysmal Afib patients with the lowest burden, those in the highest tertile had a more than threefold risk (adjusted hazard ratio 3.13; 95% CI 1.5-6.56) after adjusting for ATRIA stroke risk score, reported researchers led by Alan Go, MD, of Kaiser Permanente Northern California in Oakland.

The result was similar when the investigators adjusted for CHA2DS2-VASc stroke risk score (HR 3.16, 95% CI 1.51-6.62). The patients in the study were not on anticoagulants, and the results were consistent across subgroups of age sex, chronic kidney disease, hypertension, and diabetes, the researchers said online in JAMA Cardiology.

"According to our study, their absolute risk of stroke was about 3% per year, which is comparable to the stroke risk seen in other studies of patients with permanent atrial fibrillation who have additional risk factors for stroke," Go told MedPage Today.

Clinical Implications

Current guidelines recommend anticoagulants for stroke prevention, based on clinical risk stratification, for both non-paroxysmal and paroxysmal atrial fibrillation, the study authors noted. "Yet, little is known about whether the burden of atrial fibrillation (ie, the amount of time spent in atrial fibrillation) independently increases the risk of stroke among patients with paroxysmal atrial fibrillation, for whom decision making about stroke prevention strategies can be challenging."

In an accompanying editorial, Benjamin Steinberg, MD, of the University of Utah Health Sciences Center in Salt Lake City, and Jonathan Piccini, MD, of the Duke University Medical Center in Durham, N.C., said the study provides additional, compelling evidence of a dose-response association between the burden of paroxysmal Afib and stroke risk.

"The strengths of this analysis include a relatively long duration of continuous monitoring (14 days), a focus on [thromboembolic events] that occurred while participants were not taking anticoagulation and were verified by medical record review, and robust statistical methods," they said. "These data may have important implications for treating patients with paroxysmal AF and low CHA2DS2-VASc scores. In these low-risk patients, increased AF burden may identify those with additional and actionable stroke risk in whom the net clinical benefit of OAC [oral anticoagulants] is favorable."

Another expert not involved in the study agreed with that assessment. "These are patients with a relatively low burden of atrial fibrillation that are clearly at risk for thromboembolism based on their CHA2DS2-VASc scores, who were not anti-coagulated," Andrew Krahn, MD, chief of cardiology at the University of British Columbia in Vancouver, told MedPage Today. "Current guidelines support anticoagulation for these people, and the current study supports that they are at risk. The dose-response association noted by the authors (not risk, association) fits with the rationale that a greater amount of even infrequent AFib poses risk, and warrants anticoagulation."

Continuous Monitoring to Assess Burden

Go and colleagues retrospectively analyzed data from a cohort of 1,965 adults with paroxysmal Afib. The mean age of the cohort was 69 and nearly half (45%) were women. The mean ATRIA risk score was 4 (interquartile range 2-7) and the mean CHA2DS2-VASc risk score was 3 (IQR 1-4).

From 2011 to 2016, all patients underwent up to 14 days of continuous ambulatory electrographic monitoring using a wireless, single-patient-use monitor attached to the upper left chest. The monitor was developed by iRhythm Technologies, which funded the study.

The mean Afib burden, defined as the percentage of time in atrial fibrillation or flutter during the monitoring period, was 4.4%. In the highest tertile, the burden was 11.4% or greater.

During 1,915 person-years of follow-up, there were 29 thromboembolic events: 19 ischemic strokes, eight transient ischemic attacks, and two other arterial events identified by medical records. The investigators used Cox regression models to assess the relationship between Afib burden and stroke risk.

Go and colleagues noted some limitations of their study. Information on why the patients were undergoing arrhythmia monitoring and not receiving anticoagulants was not available. In addition, the study could not determine whether monitoring periods longer or shorter than 14 days might be useful in assessing Afib burden, they said.

Results of another study that used continuous monitoring and demonstrated the importance of Afib burden, the CASTLE-AF study, were presented last week at the Heart Rhythm Society meeting in Boston. This study focused on patients with Afib and heart failure.

"In this trial, all patients had continuous monitoring with an implantable defibrillator and underwent two types of treatments, catheter ablation or drugs. We concluded that lowering the AF burden to 5% to 10%, and not the AF recurrence, was associated with lower mortality and hospitalization rates," lead author Nassir Marrouche, MD, of the University of Utah in Salt Lake City, told MedPage Today.

"With the recent introduction and fast adoption of continuous monitoring tools such as patches, smartphone devices, wearables, and implantable loop recorders, the treatment target for managing AF should be changed to 'low AF burden' rather than just symptoms and quality of life. We have enough evidence that burden leads to increase risk of strokes, hospitalizations, and mortality," Marrouche said.

The study was funded by iRhythm Technologies.

Go disclosed no relevant financial relationships. One study author is an employee of iRhythm Technologies.

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